JP2011213500A - Method for producing carbon nanotube dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a carbon nanotube dispersion where the dispersibility of a carbon nanotube is enhanced while relaxing the condition of agitation.SOLUTION: The method for producing the carbon nanotube dispersion includes an agitating step to obtain a mixed liquid by agitating the carbon nanotube and a dispersant in a dispersing medium and an ultrasonic wave irradiating step to irradiate the mixed liquid with ultrasonic waves. The agitating step is performed under reduced pressure. For example, a cellulose-based polymer is used as the dispersant. For example, an aqueous dispersing medium is used as the dispersing medium.

Description

  The present invention relates to a method for producing a carbon nanotube dispersion capable of enhancing the dispersibility of carbon nanotubes.

  The carbon nanotube has a structure in which a hexagonal mesh graphite sheet (graphene) has a cylindrical shape. Those formed from a single layer of graphite sheet are called single-walled carbon nanotubes (SWNT), and those formed from multiple layers of graphite sheet are called multi-walled carbon nanotubes (MWNT). Since such carbon nanotubes have specific physical properties such as electrical properties, mechanical properties, and thermal properties, their application in various fields is being studied. Examples of application of carbon nanotubes include functional paints such as conductive paints and heat dissipating paints, functional resin materials such as conductive resin materials and heat dissipating resin materials, and the like. With such functional paints and functional resin materials, high-strength coating films and molded products can be obtained, and additional functions such as conductivity and heat dissipation are exhibited in the coating films and molded products. become.

  In recent years, although powdered carbon nanotubes are commercially available, such powdered carbon nanotubes are in an aggregated state, so that even if the carbon nanotubes in that state are blended with other materials, dispersibility can be improved. Have difficulty. In this regard, the carbon nanotube dispersion technique is an important technique when the carbon nanotube is used in various fields. As such a dispersion technique, although it is effective to irradiate a mixed liquid of carbon nanotubes and a dispersion medium with ultrasonic waves, there is a problem that the carbon nanotubes are fragmented (see Patent Document 1). Therefore, in Patent Document 1, without depending on only the method of irradiating ultrasonic waves, a high-speed stirring method in which a mixed liquid containing carbon nanotubes and a dispersion medium is stirred at a high rotational speed, or the inside of a stirring vessel is atmospheric pressure or A dispersion technique that uses a high-speed stirring method in a pressurized state has been proposed (see Patent Document 1).

JP 2008-195563 A

  There is a limit in trying to disperse carbon nanotubes only by the method of irradiating ultrasonic waves. Moreover, in the high-speed stirring process as described in Patent Document 1 described above, power consumption associated with stirring tends to increase. Thus, it is not preferable to make the stirring conditions harsh, and there is still room for improvement in the carbon nanotube dispersion technology.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for producing a carbon nanotube dispersion that can enhance the dispersibility of carbon nanotubes while relaxing the stirring conditions. .

  In order to achieve the above object, the method for producing a carbon nanotube dispersion of the invention according to claim 1 includes a stirring step of stirring the carbon nanotube and the dispersant in a dispersion medium to obtain a mixed solution, And an ultrasonic wave irradiation step of irradiating the mixed solution with ultrasonic waves, and the stirring step is carried out under reduced pressure.

  Here, when the carbon nanotubes come into contact with the dispersion medium and the dispersant, for example, the air present in the dispersion medium or the air attached to the surface of the carbon nanotubes has an affinity between the carbon nanotubes and the dispersion medium. This is considered to be a factor that reduces the action of the dispersant. According to the above method, since the stirring step is performed under reduced pressure, the air in the dispersion medium is reduced during stirring. Thereby, it is considered that the affinity between the carbon nanotubes and the dispersion medium is increased, and the dispersant acts efficiently on the carbon nanotubes in the dispersion medium. As a result, it is considered that the dispersibility of the carbon nanotube is enhanced.

The gist of the invention described in claim 2 is that, in the method for producing a carbon nanotube dispersion liquid described in claim 1, the cellulose-based polymer is included as the dispersant.
As the dispersant described above, for example, a cellulose polymer such as carboxymethyl cellulose is preferably used.

Invention of Claim 3 makes it a summary for the manufacturing method of the carbon nanotube dispersion liquid of Claim 1 or Claim 2 that the said dispersion medium is an aqueous dispersion medium.
Here, the carbon nanotubes are extremely advantageous in terms of enhancing the dispersibility with respect to the aqueous dispersion medium as described in claim 3 since it is difficult to obtain affinity for the aqueous dispersion medium.

  According to the present invention, it is possible to improve the dispersibility of carbon nanotubes while relaxing the stirring conditions.

Hereinafter, the embodiment which actualized the manufacturing method of the carbon nanotube dispersion liquid of the present invention is described in detail.
The method for producing a carbon nanotube dispersion according to the present embodiment includes a stirring step of stirring a carbon nanotube and a dispersant in a dispersion medium to obtain a mixed solution, and an ultrasonic irradiation step of irradiating the mixture with ultrasonic waves. including. The stirring step is performed under reduced pressure.

  The carbon nanotube (CNT) has a structure in which a hexagonal mesh graphite sheet (graphene) has a cylindrical shape. The carbon nanotube may be a single-walled carbon nanotube (SWNT) or a multi-walled carbon nanotube (MWNT). Moreover, the carbon nanotube which included fullerene may be sufficient. The method for producing the carbon nanotube is not particularly limited, and examples thereof include an arc discharge method, a laser evaporation method, and a chemical vapor deposition method.

  The diameter of the carbon nanotube is preferably in the range of 1 nm to 500 nm. The ratio of the length to the diameter of the carbon nanotube, that is, the aspect ratio of the carbon nanotube is not particularly limited, but is, for example, about 10 to 10,000. The length of the carbon nanotube is, for example, about 0.1 μm to 100 μm.

  The type of the dispersion medium is not particularly limited and is appropriately selected depending on the use of the carbon nanotube dispersion. Here, since it is difficult for carbon nanotubes to have an affinity for an aqueous dispersion medium, there is an increasing demand for improving the dispersibility of such an aqueous dispersion medium. From this point of view, the production method of this embodiment is extremely advantageous in producing a carbon nanotube dispersion using an aqueous dispersion medium as a dispersion medium.

  Examples of the aqueous dispersion medium include water, a water-soluble organic solvent, and a mixed liquid of the water-soluble organic solvent and water. Examples of the water-soluble organic solvent include alcohols, glycols, polyhydric alcohols, glycol ethers, ketones, esters, amides, halogenated hydrocarbons, and other water-soluble organic solvents. Examples of alcohols include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and octanol.

  Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol.

Examples of the polyhydric alcohols include glycerin, trimethylolpropane, pentaerythritol, and sorbitol.
Examples of glycol ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether. Examples include ethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

Examples of ketones include acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.
Examples of the esters include ethyl acetate, γ-butyllactone, and ε-propyrolactone. Examples of amides include N, N-dimethylformamide, N, N-dimethylacetamide, and N-methylpyrrolidone. Examples of halogenated hydrocarbons include dichloromethane, chloroform, and dichloroethane. Other water-soluble organic solvents include tetrahydrofuran, dimethyl sulfoxide, tetramethylene sulfoxide, acetonitrile, and propionitrile.

These water-soluble organic solvents may be used alone or in combination of two or more.
A dispersing agent is not specifically limited, For example, according to the kind of dispersion medium, the kind of carbon nanotube, etc., it can select suitably. Specific examples of the dispersant include a surfactant and a water-soluble polymer. Examples of the surfactant include an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant.

  Examples of the anionic surfactant include carboxylate, sulfonate, sulfate ester salt, and phosphate ester salt. Examples of the cationic surfactant include alkyl trimethyl ammonium salt, alkyl dimethyl ammonium salt, and alkyl dimethyl benzyl ammonium salt. Examples of the nonionic surfactant include polyoxyethylene alkylphenol ether, polyoxyethylene alkyl ether, and polyoxyethylene fatty acid ester. Examples of amphoteric surfactants include betaine amphoteric surfactants, amino amphoteric surfactants, and imidazoline surfactants.

Examples of the water-soluble polymer include ether polymers, vinyl polymers, acrylamide polymers, cellulose polymers, and starch polymers. Examples of the ether-based polymer include polyethylene oxide. Examples of the vinyl polymer include polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether. Examples of the acrylamide polymer include polyacrylamide. Examples of the cellulose polymer include methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose. Examples of the starch-based polymer include oxidized starch and gelatin.

  These dispersants may be used alone or in combination of two or more. Moreover, you may mix | blend a dispersing agent as a salt. Among the dispersants, for example, a cellulose-based polymer is preferably used.

  In the stirring step, various additives such as an antioxidant, a viscosity modifier, an antifoaming agent, an ultraviolet absorber, and a colorant may be blended as components other than the carbon nanotubes, the dispersant, and the dispersion medium.

  The blending amount of the dispersion medium with respect to the carbon nanotubes is, for example, in the range of 50 to 10,000 parts by mass with respect to 1 part by mass of the carbon nanotubes. Moreover, the compounding quantity of the dispersing agent with respect to a carbon nanotube shall be the range of 0.1-100 mass parts with respect to 1 mass part of carbon nanotubes.

  In the stirring step, the above-described carbon nanotubes and a dispersant are mixed in a dispersion medium. Here, when the carbon nanotubes come into contact with the dispersion medium and the dispersant, for example, the air present in the dispersion medium or the air attached to the surface of the carbon nanotubes has an affinity between the carbon nanotubes and the dispersion medium. This is considered to be a factor that reduces the action of the dispersant.

  In this regard, by carrying out the stirring step under reduced pressure, the air in the dispersion medium is reduced during stirring. Thereby, it is considered that the affinity between the carbon nanotubes and the dispersion medium is increased, and the dispersant acts efficiently on the carbon nanotubes in the dispersion medium. As a result, it is considered that the dispersibility of the carbon nanotube is enhanced.

  The stirring device used in the stirring step is not particularly limited, and examples thereof include a homogenizer, a spiral mixer, a planetary mixer, a ball mill, and a kneader in addition to a stirring device having a propeller type stirring blade. Since the stirring step of the present embodiment is a method for improving the dispersibility of the carbon nanotubes by carrying out under reduced pressure, the stirring conditions can be relaxed. For this reason, sufficient dispersibility can be obtained even if the rotational speed is relatively slow using, for example, a propeller type stirring device. The rotation speed of the stirring device is, for example, 50 to 500 rotations / minute, and the stirring time can be, for example, in the range of 5 minutes to 30 minutes.

  By performing the stirring step under reduced pressure, degassing of the mixed liquid containing the carbon nanotubes, the dispersant, and the dispersion medium proceeds. Here, under reduced pressure in the stirring step refers to a pressure condition lower than atmospheric pressure. Examples of the decompression device used in the stirring step include a vacuum pump and an aspirator. The pressure in the stirring step is preferably 50 kPa or less, more preferably 30 kPa or less, and further preferably 20 kPa or less. In addition, it is preferable that the minimum of a pressure is 5 kPa or more, for example. In the stirring step, the temperature of the mixed liquid may be adjusted from the viewpoint of preventing the dispersion medium from boiling and coagulating. For example, according to the pressure, the stirring step can be easily performed by adjusting the temperature range below the boiling point of the dispersion medium and above the freezing point of the dispersion medium.

  In the ultrasonic irradiation step, the dispersion of the carbon nanotubes in the dispersion medium is promoted by irradiating the mixed liquid with ultrasonic waves. Although the ultrasonic irradiation conditions are not particularly limited, for example, the frequency is in the range of 10 kHz to 150 kHz, the amplitude is in the range of 5 to 100 μm, for example, and the irradiation time is in the range of 1 to 300 minutes, for example. In the ultrasonic irradiation step, the temperature of the mixed solution may be adjusted from the viewpoint of suppressing the volatilization of the dispersion medium. As an ultrasonic generator, what is marketed as an ultrasonic homogenizer etc. can be used, for example.

  The use of the dispersion obtained through the stirring step and the ultrasonic irradiation step is not particularly limited. For example, paint, adhesive, lubricant, ink, battery additive, concrete or mortar additive, fiber binder additive. Can be mentioned.

The effects exhibited by this embodiment will be described below.
(1) The method for producing a carbon nanotube dispersion of this embodiment includes a stirring step of obtaining a mixed solution by stirring carbon nanotubes and a dispersing agent in a dispersion medium, and an ultrasonic wave that irradiates the mixed solution with ultrasonic waves. Irradiation step. Since the stirring step is performed under reduced pressure, the dispersibility of the carbon nanotubes can be improved.

(2) As a dispersing agent mix | blended in a stirring process, a cellulose polymer is used suitably, for example.
(3) Since it is difficult for carbon nanotubes to obtain an affinity for an aqueous dispersion medium, the production method of this embodiment is extremely advantageous in terms of enhancing the dispersibility for an aqueous dispersion medium.

In addition, the said embodiment can also be changed and comprised as follows.
The stirring step may be performed while maintaining a substantially constant pressure or may be performed while changing the pressure. For example, it is easy to prevent the dispersion medium from boiling by performing the stirring step while gradually reducing the pressure.

-As a pre-process of the said stirring process, you may stir under atmospheric pressure or the pressure higher than atmospheric pressure.
-When performing the said ultrasonic irradiation process, the conditions of a pressure are not specifically limited. Note that the ultrasonic irradiation step may be performed under reduced pressure as in the stirring step.

Next, the technical idea that can be grasped from the above embodiment will be described below.
(A) The said stirring process is a manufacturing method of the carbon nanotube dispersion liquid implemented by the rotation speed of 500 rotations / min or less using a propeller-type stirring apparatus. In this way, the stirring conditions can be relaxed.

  (B) A method for producing a carbon nanotube dispersion in which the pressure in the stirring step is 50 kPa or less.

Next, the embodiment will be described more specifically with reference to examples and comparative examples.
Example 1
Carbon nanotubes (manufactured by Showa Denko KK, trade name: VGCF-S) and carboxymethyl cellulose as a dispersant (trade name: CMC1105, trade name: CMC1105) are blended in ion-exchanged water as a dispersion medium, and a reduced pressure of 8 kPa. Below, the liquid mixture was prepared by implementing a stirring process by stirring using a propeller mixer (The product name: NRXM-200B by the simpo industry company). In addition, while content of the carbon nanotube in a liquid mixture is 1 mass%, content of a dispersing agent is 1 mass%. The stirring conditions were 190 rpm / minute and 10 minutes.

  By irradiating the mixed solution obtained by the stirring process with ultrasonic waves using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., US-1200CVR) under the conditions of a frequency of 20 kHz, an amplitude of 50 μm, and 120 minutes, An irradiation process was performed.

  The particle size distribution of the obtained carbon nanotube dispersion was measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, trade name: SALD-2000J). Table 1 shows the average particle size calculated from the particle size distribution.

(Comparative Example 1)
In Comparative Example 1, a carbon nanotube dispersion was produced in the same manner as in Example 1 except that the stirring step was performed under atmospheric pressure. For this carbon nanotube dispersion, the average particle size was calculated from the particle size distribution in the same manner as in Example 1. The results are shown in Table 1.

(Evaluation of dispersion stability)
The carbon nanotube dispersion liquid of each example was allowed to stand at a temperature of 23 ° C. for 5 hours, and then visually observed for the presence or absence of carbon nanotube precipitation. The results are shown in Table 1.

表１に示されるように、比較例１では、２３℃で５時間静置後に沈殿が生じていた。これに対して、実施例１では、２３℃で５時間静置後においても沈殿は生じていなかった。なお、実施例１の平均粒子径は、比較例１よりも小さいことから、実施例１では比較例１よりもカーボンナノチューブの分散性が高まっていることが分かる。

As shown in Table 1, in Comparative Example 1, precipitation occurred after standing at 23 ° C. for 5 hours. On the other hand, in Example 1, no precipitation occurred even after standing at 23 ° C. for 5 hours. In addition, since the average particle diameter of Example 1 is smaller than Comparative Example 1, it can be seen that in Example 1, the dispersibility of carbon nanotubes is higher than that of Comparative Example 1.

Claims (3)

An agitation step of obtaining a mixed liquid by agitating the carbon nanotube and the dispersant in the dispersion medium;
An ultrasonic irradiation step of irradiating the mixture with ultrasonic waves,
The method for producing a carbon nanotube dispersion liquid, wherein the stirring step is performed under reduced pressure. The method for producing a carbon nanotube dispersion liquid according to claim 1, wherein the dispersant contains a cellulose-based polymer. The method for producing a carbon nanotube dispersion liquid according to claim 1, wherein the dispersion medium is an aqueous dispersion medium.